Allowing networks to be specified at launch in the dashboard

OS-252

Adds support for specifying the networks to attach to the launched
instance in the dashboard. Note: similar to the boot workflow, a
network must be specified when using the dashboard. This also only
applies when Quantum/Neutron is used for networking.

Change-Id: I5f4dec4d7baf25de6ff697d6829d5efab4f6a2f7
Merge "Allowing networks to be specified at launch in the dashboard" into grizzly/1.4